1. Field of the Invention
The present invention relates to an image forming device that is preferably used in a copier, a printer, and a facsimile machine etc. In particular, the present invention relates to an image forming device that forms images by using two-component developer including toner and carrier.
2. Description of the Related Art
An image forming device that forms images by the following image forming processes is known as an electrophotographic image forming device using a photoconductive drum, for example, as an image carrier. A surface of the photoconductive drum is charged and exposed to form an electrostatic latent image. Toner is adhered to the electrostatic latent image, and the image is visualized as a toner image. Then, the toner image is transferred to a paper, and the transferred toner image is fixed to the paper.
Two types of developer, two-component developer and one-component developer, have been conventionally used as the developer that is used to form an image. The two-component developer includes toner and carrier, which is composed of magnetic particles. The one-component developer includes only the toner. When using the two-component developer, the toner and the carrier are rubbed against each other, and the toner can be charged in good condition. Therefore, high-resolution image forming can be stably performed. In an image forming device using such two-component developer, it is required to maintain a steady mixture ratio of the toner and the carrier in the developer. Therefore, toner concentration is constantly detected, and toner supply is controlled in order that the toner concentration is kept within a predetermined range. A toner-concentration detecting process has been conventionally performed as follows. A conventional image forming device includes a main drive motor, a development driving mechanism, which supplies a developer flowing mechanism with power after the main drive motor, and a control device. In accordance with history data based on an operation history of electrophotographic processes, the control device controls timing that indicates a time interval between a start time of an operation of the development driving mechanism and a time of reading a toner concentration signal. And then, the control device reads the toner concentration signal.
Immediately after a transporting operation of the two-component developer is started after the transporting operation has been stopped, an amount and density of the developer are not stable. Accordingly, since an output signal from a toner-concentration detecting sensor greatly changes, toner concentration cannot be detected accurately. Under such a state, when the toner supply is controlled based on the detection signal, an appropriate amount of toner is not supplied. Therefore, in the conventional image forming device, the developer transporting operation is not performed until detection output of the toner concentration becomes stable.
Accordingly, upon a preparation operation performed when a power supply of the image forming device is turned on, or upon an image forming operation for the first paper performed when the image forming processes are started, the following control is performed. That is, the control device starts driving the photoconductive drum etc. along with the developer transporting operation at timing when a fixing temperature reaches a predetermined temperature. However, in the conventional image forming device, a problem is that, since it takes time until the detection output of the toner concentration becomes stable, the subsequent processes will be delayed.